On crowded days the FastPass-tickets may sell out quiet soon, so turn up early at the FastPass-attractions, but always keep in mind that you won't be able to turn in a FastPass-ticket before the indicated time so think twice before taking a FastPass as you wont be able to get a second FastPass for another attraction till the time-window of the first one has turned up.
To get a second FastPass as early as possible for the same or another attraction, go to the FastPass-machines and take a second FastPass-ticket as soon as the time indicated on your first FastPass-ticket has arrived (the FastPass-machines only check that the time-window of the FastPass-ticket issued earlier has arrived, but not whether you used it), only after this proceed to the attraction and take use of the first FastPass-ticket.
Don't worry if there is a line at the FastPass-entrance to the attraction. A possible reasons could be, that a breakdown of the ride earlier has resulted in people from several time-windows lining up - the castmembers will reduce the FastPass-line as fast as possible. But there is a second more common cause for lines at the FastPass-entrance: guests show up before their reserved time-window and are turned back by the castmember at the entrance and then form a line beside the entrance to wait for their time-window to arrive. So there is no sense in showing up too early, you won't be allowed to enter the attraction. If you are on time and there is a line check out with the castmember at the entrance which of the two causes resulted in the line building up. As said, most common is the second one, so you could enter the attraction without waiting if you are on time.
Want to collect FastPass-tickets as free souvenirs? Please: don't take a FastPass-ticket and let it expire without using it. Keep in mind: the number of FastPass-tickets for each time-window is limited so someone else would have to wait longer. Instead try to get a second FastPass-ticket before the time-window of the first one arrives. The machine will then print out a non valid-FastPass-ticket on the usual FastPass-ticket-forms you wanted to collect.
One last whish: if you got a FastPass-ticket and don't want to use it - please hand it on to guests in the Stand-By-Line, they will be happy!